Soft gel capsules have been widely known and used for many years and for a variety of purposes. Soft gel capsules are quite different from hard-shell capsules, in that they are formed, filled and sealed in a one step process from a plasticized shell material incorporating desired functional properties, and a wide range of liquid fill materials that may be hydrophilic, hydrophobic or combinations thereof. It is well known in the art to use soft gel capsules to contain materials for oral consumption, such as vitamins, nutritional supplements and active pharmaceutical ingredients that are specially formulated in liquid vehicles or carriers for soft gel encapsulation.
However, not all liquids can be used as the only vehicle or carrier in soft gel capsules. Liquids such as water, propylene glycol, glycerin, low molecular weight alcohols, ketones, acids, amines and esters can be used only with other liquids to prepare vehicles or carriers in soft gel capsules, known in the art as fill formulations. Such liquids may be used as functional components of soft gel fill material.
A limitation in the use of soft gel capsules is that it may not be possible to formulate the active pharmaceutical ingredient in a volume of solvent small enough to produce a soft gel capsule that delivers the desired dosage amount and is economically appropriate and comfortable to ingest by the patient. This limitation is particularly relevant when a clear solution or dispersion of the pharmaceutical agent is desired. One such pharmaceutical agent is naproxen, which is poorly soluble in water and has limited solubility in the combinations of ingredients typically used for soft gel capsule fill materials.
Naproxen is a non-steroidal anti-inflammatory drug (NSAID) that is commonly used to relieve pain and to treat inflammatory conditions. Naproxen, (+)-(S)-2-(6-methoxynaphthalen-2-yl)propanoic acid, is a member of the 2-arylpropionic acid (profen) family of NSAID's. Naproxen and other NSAID's are practically insoluble in water. The solubility of naproxen in liquids and combinations of liquids that are suitable vehicles or carriers in soft gel capsules is insufficient to provide a reasonably sized capsule. In particular, the solubility of naproxen in polyethylene glycol, the preferred vehicle or carrier for hydrophilic active ingredients, is insufficient to provide a reasonably sized capsule small enough to be comfortably administered to most patients.
Several processes have been developed in efforts to increase the solubility, and, hence, the bioavailability of naproxen. One such prior art process is disclosed by Yu et al. in U.S. Pat. Nos. 5,071,643 and 5,360,615, both of which disclose the use of a water-based solvent system for enhancing the solubility of an acidic pharmaceutical agent, such as naproxen, to produce a highly concentrated solution suitable for encapsulation in soft gel capsules. The solvent system disclosed includes 10% to 80% by weight polyethylene glycol, 1% to 20% by weight water and hydroxide ion species. The solvent systems provide for a highly concentrated solution capable of encapsulation into a small vessel, such as a soft gel capsule, to permit easy swallowing and to provide a pharmaceutically effective dose of a pharmaceutical agent, such as naproxen. The method disclosed in the Yu et al. references the formation of a solution of the pharmaceutical agent (naproxen) in a water-based solvent system utilizing a solubility-enhancing agent such as sodium hydroxide, ammonium hydroxide or potassium hydroxide to solubilize the naproxen by partial neutralization. Tindal et al. discloses another prior art process in U.S. Pat. No. 6,387,400, for increasing the concentration of a pharmaceutically active ingredient for dosage units of soft gel capsules. This disclosure describes a process for ibuprofen and refers to other acidic compounds such as naproxen. The method disclosed by Tindal et al. is based on the preparation of a solution of the pharmaceutical agent in polyethylene glycol and a hydroxide ion source through a process based on the gradual and incremental addition of the pharmaceutical agent and the hydroxide ion source.
A further limitation to the use of certain liquids as vehicles or carriers for soft gels are is the pH value of the liquid as taught by Yu et. al., in U.S. Pat. No. 5,360,615. For example, the pH of the fill liquid should not be below 2.5 or above 7.5. At pH values below 2.5, the gelatin may be hydrolyzed causing leaking, whereas at pH's greater than 7.5, the gelatin is tanned resulting in decreased solubility of the gelatin shell.
Naproxen and naproxen sodium are recognized active pharmaceutical ingredients and the subject of monographs in the USP. Naproxen sodium is a recognized sodium salt form of naproxen. Although naproxen sodium is highly soluble in polyethylene glycol, the use of the more soluble naproxen sodium presents other problems. When naproxen sodium is solubilized in polyethylene glycol, the resulting solution is alkaline, which is corrosive to the soft gel shell. Thus, naproxen sodium is unsuitable for soft gel encapsulation.
The prior art teaches the use of polyethylene glycol and hydroxide ion source to solubilize pharmaceutical agents, such as naproxen and ibuprofen. However, the addition of a hydroxide ion source, such as sodium hydroxide, ammonium hydroxide or potassium hydroxide, to neutralize the solution results in an increase in overall volume of the fill material. Increasing the concentrations of active ingredients, such as naproxen, naproxen sodium or other NSAID's, in soft gel dosage forms and/or units without necessitating an increase in overall volume of the fill material (and thereby increasing overall size of the dosage form) and/or without an increase disintegration or dispersion of the capsule shell have proven difficult to accomplish in the art.
As shown in the prior art, the ability to adjust the pH of fill formulations is problematic without additional process steps. The prior art teaches to neutralize the solution containing the active ingredient through numerous addition steps using a hydroxide ion source, such as sodium hydroxide, ammonium hydroxide or potassium hydroxide. The ability to adjust the pH values of fill formulations is particularly relevant to combinations of NSAID's, such as naproxen, and other active pharmaceutical ingredients, such as phenylephrine hydrochloride, doxylamine succinate and dextromethorphan hydrobromide, where the solubility or stability of the other active ingredient may be optimized by adjusting the pH of the fill formulation (or neutralizing the acidic/basic API).
It would be advantageous and desirable to provide pharmaceutical formulations of NSAID's, such as naproxen, for encapsulation in soft gels, which produces a solution that accommodates higher concentrations of the active ingredient than previously described without increasing the overall size of the dosage form. Such pharmaceutical formulations would permit a reduction in overall size of the dosage form. It is also desirable to provide pharmaceutical formulations of NSAID's, such as naproxen, based on polyethylene glycol to provide a reasonably sized capsule that is not corrosive to the soft capsule shell.
It would also be advantageous and desirable to have improved processes to produce pharmaceutical formulations of naproxen and other NSAID's having adjustable pH values without needing to neutralize the solution containing the active ingredient through numerous addition steps. The elimination of the neutralization process permits a more economical and controllable manufacturing process. Also, the elimination of a corrosive or caustic adjuvant such as sodium hydroxide provides a much safer process for the workplace.